The present invention relates to a battery saving signal generating circuit, and more particularly to a signal generator suitable for a battery saving system for saving energy of a battery assembled in a paging receiver, e.g., a pocket bell.
Paging receivers such as pocket bells ordinarily use a small battery as a power source. Since the current capacity of the battery used is limited to a specified value, the battery must be exchanged with a new one each time that its energy is exhausted. In such paging receivers, it is required to save current consumption as far as possible in order to reduce the troublesome battery exchange. For this purpose, e.g., a Battery Saving System (which will be called "BSS" hereinafter) has been employed.
In conventional paging receivers adapted to receive a calling signal which is carried by a radio carrier wave and transmitted from a transmitter base station, wasteful current consumption is suppressed by making use of the above-mentioned BSS when the calling signal is not being transmitted, i.e., when the receiver is in a waiting condition. Namely, as seen from a time chart shown in FIG. 1, the power supply of the receiver is turned on only during time slots TW.sub.1 produced at predetermined time intervals TD.sub.1 and turned off for a time except for the time slot. Further, when a calling signal S is desired to be transmitted from the transmitter base station, a preamble signal P as shown at section (b) in FIG. 2 is transmitted as a signal which precedes the calling signal S. Accordingly, the receiver receives and detects the preamble signal within a time slot TW.sub.2 as shown at (a) in FIG. 2, so that the BSS condition can be released to turn on power supply for a time period TW.sub.2 ', thereby ensuring reception of the subsequent calling signal.
Conventionally, since, in the BSS bit rate and signal length TP, TS of each of the preamble signal P and the calling signal S are constant, it is sufficient that the time width TW.sub.2 of the BSS time slot and its occurrence time interval TD.sub.2 are constant. For this reason, the time width TW.sub.2 and the occurrence time interval TD.sub.2 can be determined by the common use of a single frequency divider circuit.
Recently, however, in proportion to an increase in the number of paging subscribers in the paging receiver system, the frequency of transmission of calling signals increases per unit of time. Accordingly, it has been required to shorten the bit rate and the signal length TP of the preamble signal P as far as possible and to narrow the occurrence time interval of the BSS time slot. As stated above, in the conventional BSS, the time width of the BSS time slot and its occurrence time interval have been determined by the common single frequency divider circuit. For this reason, the drawbacks with such a conventional BSS is that since there is a limitation upon the determination of the time width of the BSS time slot and the occurrence time interval thereof, it is impossible to independently select them, resulting in an impairment of the adaptability to the above-mentioned presently available paging system using preamble signals of different lengths.